1. Field of the Invention
The present invention relates to the field of asphalt emulsions and improvers therefore, commonly classified in U.S. Patent Office Class 106, Subclass 277 or Class 260, Subclasses 28R and 28.5.
2. Description of the Prior Art
Among the wide variety of formulation problems constantly faced by the asphalt road building industry and its suppliers with respect to asphalt-in-water emulsions are:
A. Viscosity (ASTM D244 test). PA1 B. Storage stability (ASTM D244), the ability to maintain the integrity of the emulsion by prevention of settling and/or creaming in which ingredients selectively move to the bottom or top respectively). PA1 C. Coating ability (ASTM D244), the ability to coat the particles of the road-building aggregate. PA1 D. Demulsibility, (ASTM D244), ability of the emulsion to break in the presence of polyvalent metals and other demulsification agents so as to "set" in the presence of stone or calcium chloride. PA1 E. Sieve, (ASTM D244), resistance to agglomeration between the individual particles in the emulsion with consequent settling and loss of homogenity). PA1 F. Viscosity Maintenance: (change in ASTM D244 viscosity with time), the prevention of substantial fluctuations in viscosity during storage of the asphalt emulsions.
The prior art has addressed quite thoroughly each of the first three of the problems listed above, i.e. viscosity, storage stability, coating ability.
For example various solutions to the problem have been taught by U.S. Patents as follows: U.S. Pat. No. 3,785,852 to Schleidt which teaches use of polyvinyl alcohol as a stabilizer for a bituminous emulsion (e.g. column 2, line 60+); U.S. Pat. No. 2,941,893 to McConnaughay which teaches asphalt emulsions containing hydroxypropylmethyl cellulose (e.g. column 1, lines 47+); U.S. Pat. No. 3,843,576 to Parkinson which discloses using an ethylene-acid copolymer in a composition also containing a phenolic resin and coal tar pitch or the like in the form of dispersions (e.g. column 5, lines 34+); U.S. Pat. No. 4,176,102 to Favata which teaches acrylic-acid polymers and p. 192 of volume 1 of the 1964 edition of Encyclopedia of Polymer Science and Technology, Table 5, which discloses use of polyacrylamides as "emulsion stabilizers and thickening agents".
However, the remaining three problems listed above have continued to trouble the industry and to produce serious defects in roads prepared with asphalt emulsions under particularly adverse weather conditions. For example, demulsibility characteristics have frequently proven insufficient in otherwise satisfactory asphalt emulsions and have permitted a loss of aggregate in roads subjected to heavy rains prior to their having been fully set in the presence of stone and other aggregate components.
Also, because asphalt emulsions are often prepared on a seasonal basis and must be therefore frequently stored for relatively long periods prior to use, segregation or lessening of viscosity may cause emulsions which were of good quality when manufactured to fall below industry specifications after prolonged storage. Viscosity increases during storage can deter the application of the asphalt emulsions by conventional spraying techniques and viscosity decreases can sharply reduce the bonding and coating characteristics of the asphalts when applied to the aggregates. Where the viscosity is too low (the asphalt emulsion is too "thin"), the asphalt emulsion may itself run off the road, away from the aggregate and destroy surrounding vegetation.
The importance of "sieve" should not be underestimated--low viscosity asphalt emulsions often exhibit a tendency to segregate due to agglomeration of individual particles within the emulsion and consequent settling and/or nozzle-plugging of the distributors used for applying the emulsion to the road bed.
The basic method of attainment of desired viscosity is the addition of higher percents of asphalt to the emulsion. Alternatively, and at much lower cost, aqueous sodium chloride can be injected into a non-polar, asphaltic emulsion medium to increase the viscosity of the asphalt emulsion.